The present invention relates to an oil-cooled alternator and a method of cooling an alternator driven by an internal combustion engine.
Alternators driven by an internal combustion engine of, for example, an automobile or a small ship are usually cooled by a flow of air generated by a cooling fan, and in, for example, Japanese Patent unexamined publication no. 62-225,146, a alternator is proposed wherein liquid-cooled cooling water circulated in an internal combustion engine is employed to cool the alternator.
Cooling by air, however, is disadvantageous in that the size of the alternator to be cooled becomes large and in that noise is generated by the flow of air. Cooling by the cooling water also is undesirable because the rotary part of the alternator encounters a greater resistance and the weight of the whole system is inconveniently increased.
Recently, a cooling system has been proposed in which a cooling liquid passage is formed in the rotor shaft so that a cooling liquid is distributed by the centrifugal force so as to cool, for example, the stator core of an alternator. This method, however, requires a complicated machining for forming the liquid passage and, in addition, the cooling effect is liable to be impaired by, for example, clogging of the liquid passage.